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critical resistance value. Convert the value for the current winding temperature at the time
of measurement, see above table.
Measuring the polarization index
1. To determine the polarization index, measure the insulation resistances after one minute
and ten minutes.
2. Express the measured values as a ratio:
PI =
Many measuring devices display these values automatically following the measurement.
For insulation resistances > 5000 MΩ, the measurement of the PI is no longer meaningful
and consequently not included in the assessment.
NOTICE
Damage to insulation
If the critical insulation resistance is reached or undershot, this can damage the insulation
and cause voltage flashovers.
• Contact the service center (Page 141).
• If the measured value is close to the critical value, you must subsequently check the
See also
Insulation resistance and polarization index (Page 50)
Limit values of the anti-condensation heating insulation resistance
The insulation resistance of the anti-condensation heating with respect to the machine
housing should not be lower than 1 MΩ when measured at 500 V DC.
1MB155 / 1MB555
Operating Instructions, 03/2018, A5E41926185A
R
R
/
insul 10 min
insul 1 min
R
/ R
(10 min)
(1 min)
≥ 2
< 2
insulation resistance at shorter intervals.
Assessment
Insulation in good condition
Dependent on the complete diagnosis of the insulation
Assembly
5.1 Preparations for installation
53
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